The present invention relates generally to optical fiber arrays. More particularly, the present invention relates to an optical fiber array having grooves in a front face of the array. The grooves control the flow of glue when the array is glued to an integrated optic (IO) chip so that glue is not present in the optical path between the optical fiber and IO waveguide.
Integrated optic (IO) devices are used for optical routing, switching, and modulating of optical signals. Integrated optic devices have an optical waveguide disposed on a chip. In order for an IO device to be useful, light from other waveguides (e.g. optical fibers) must be coupled into and out of the IO waveguides. Optical fibers are often coupled to an IO device by mounting several fibers in an array, and then gluing the array to terminal ends of the IO waveguides at an edge of the IO device. Many fibers can be simultaneously aligned in this manner.
FIG. 1 shows a side view of a typical combination of IO device and fiber array according to the prior art. The fiber array and IO chip are glued together (e.g. using UW-curable epoxy) so that the optical fibers are aligned with the waveguides. The IO chip has a mounting block so that the entire front face surface of the fiber array is glued to the IO chip.
The device of FIG. 1 is made by carefully aligning the fiber array and IO chip (so that IO waveguides and fibers are coupled), and then applying the glue. The glue is liquid and so flows into the narrow space between the fiber array and IO chip by capillary action. The glue is then cured by UV exposure or heat.
A problem with the device of FIG. 1 is that the glue flows between the optical fibers and the waveguides. A thin layer (e.g. 0.5-5 microns thick) of glue therefore lies in the fiber-waveguide optical path. This is undesirable in high-performance devices because the glue can interfere with (e.g. absorb or scatter) light signals. Also, the glue used should (1) have stable optical properties, (2) be index-matched to the waveguides/fibers, and (3) be optically clear. Such optical properties may not be compatible with other desirable glue properties such as high strength, low shrinkage, low creep and humidity tolerance.
U.S. Pat. No. 5,481,632 to Hiradi et al. teaches a structure for connecting fiber arrays and integrated optic waveguides. The fibers are recessed so that they do not rub against the IO chip during alignment. This prevents the fiber endfaces from becoming damaged.
U.S. Pat. No. 5,513,290 to Ishikawa et al. teaches a structure for connecting fiber arrays and integrated optic waveguides. A portion of the fiber array is made of a material that is UV-transparent. This allows UV light to access UV-curable adhesive between the IO chip and fiber array.
U.S. Pat. No. 5,446,815 to Ota et al. teaches an optical collimator array having an optical fiber array and collimating lenses. The collimating lenses have a recessed portion so that the lenses are spaced apart from the optical fibers.
Therefore, it would be an advance in the art to provide an optical fiber array-IO chip coupling arrangement that prevents glue from flowing into the optical path between the optical fibers and waveguides. Such an arrangement would enable a wide variety of adhesives to be used, and would enhance the operation of high-performance optical devices.
Accordingly, it is a primary object of the present invention to provide an optical fiber array-IO chip coupling arrangement that:
1) prevents the flow of adhesive into the optical path; and
2) is compatible with a wide variety of adhesives, including opaque solders and glues, and adhesives having very poor optical properties (e.g. low transmissivity, high birefringence, high scattering, uncontrolled refractive index).
These and other objects and advantages will be apparent upon reading the following description and accompanying drawings.
These objects and advantages are attained by an optical fiber array having a fiber array chip and an optical fiber attached to the chip. The chip has a front face with a wick stop groove that separates a bonding area and a nonbonding area. The optical fiber has an endface coplanar with the front face, and the fiber endface is disposed in the nonbonding area.
In operation, the front face is pressed against an integrated optic (IO) chip (or other optical device) and liquid adhesive is applied to the bonding area. The capillary flow of the liquid adhesive is blocked by the wick stop groove so that the adhesive does not flow between the optical fiber and a waveguide on the IO chip.
Preferably, the invention includes an IO chip bonded to the bonding area of the fiber array chip.
Also preferably, the fiber array chip comprises single crystal silicon with an anisotropically etched V-groove. The optical fiber is disposed in the V-groove.
The wick stop groove can be a dicing saw cut groove. The wick stop groove can have a width in the range of about 25-500 microns, and a depth in the range of about 5-500 microns. The best size and shape of the wick stop groove depend upon the wetting characteristics of the array chip material and adhesive used.
The wick stop groove can also be formed by bonding a stepped block to the fiber array. A step in a front face of the block provides the wick stop groove.
The fiber array can also have several intersecting wick stop grooves. The wick stop grooves may surround the fiber.
Also, the wick stop groove can be formed by a trench for holding the fiber (e.g. an anisotropically etched V-groove in silicon) having a widened front portion.
Also, the wick stop groove can be located on an IO chip. An IO chip with a wick stop groove can have any of the features described for fiber arrays with a wick stop groove.
Also, the present invention applies generally to any optical apparatus having two bonded optical devices where one device has a wick stop groove, a bonding area, and a nonbonding area. An optical path extends between the optical devices and through the nonbonding area. The wick stop groove prevents the flow of adhesive into the optical path. The optical devices can include fiber arrays, lens arrays, filters, light sources, modulators, sensors and the like.
Also, the present invention includes an embodiment where the bonding area is recessed compared to the nonbonding area. This provides a volume of controlled thickness for adhesive even when the nonbonding areas are in direct contact.